1. Field of the Invention
The present invention relates to a printing apparatus and ink discharge state determination method, and particularly to a printing apparatus using a printhead including a heating element (heater) for discharging ink, and an ink discharge state determination method.
2. Description of the Related Art
Of inkjet printing methods of discharging an ink droplet from a nozzle to attach it to paper, a plastic film, or another printing medium, there is an inkjet printing method using a printhead including a heater which generates heat energy to discharge ink. For a printhead complying with this method, for example, an electrothermal transducer which generates heat in accordance with energization, a driving circuit for it, and the like can be formed using the same process as a semiconductor manufacturing process. This printhead has advantages in which, for example, high density integration of nozzles is easy and high printing resolution can be achieved.
In this printhead, an ink discharge failure sometimes occurs in all or some nozzles of the printhead owing to a cause such as clogging of a nozzle by a foreign substance, highly viscous ink, or the like, a bubble entering an ink supply channel or nozzle, or a change of the wettability of the nozzle surface. To avoid degradation of the image quality when such discharge failure occurs, it is desirable to quickly execute a recovery operation of recovering an ink discharge state, or a complementary printing operation using another nozzle or the like. However, to quickly perform these operations, it is very important to accurately, appropriately determine an ink discharge state and occurrence of discharge failure.
There have conventionally been proposed various ink discharge state determination methods, complementary printing methods, and apparatuses to which these methods are applied.
Japanese Patent Laid-Open No. 2009-083227 discloses a method of detecting an ink flow in a channel that is generated when discharging ink, in order to detect an ink discharge failure. In Japanese Patent Laid-Open No. 2009-083227, the discharge state is determined using the fact that the ink flow is small upon occurrence of discharge failure, compared to normal discharge. As the method of detecting an ink flow, Japanese Patent Laid-Open No. 2009-083227 discloses a method of regarding an ink flow as heat transfer of ink and detecting a change of the temperature of heat-applied ink, and an arrangement in which a sensor for detecting a temperature is arranged in the channel or nozzle.
Japanese Patent Laid-Open No. 2008-000914 discloses a method of detecting a temperature drop generated in normal discharge in order to detect discharge failure. According to Japanese Patent Laid-Open No. 2008-000914, in normal discharge, a point at which the temperature drop rate changes appears a predetermined time after a detected temperature reaches a maximum temperature. However, when discharge failure occurs, this point does not appear. By detecting the presence/absence of this point, the ink discharge state is determined. Japanese Patent Laid-Open No. 2008-000914 also discloses an arrangement in which a temperature detector is arranged below a heater configured to generate heat energy for discharge. As a method of detecting the presence/absence of the point, Japanese Patent Laid-Open No. 2008-000914 also discloses a method of detecting the point as a peak value by differential processing.
However, the discharge state determination method disclosed in Japanese Patent Laid-Open No. 2009-083227 utilizes a difference in ink flow, and the detector is arranged at a location spaced apart from the heater. Thus, a large difference is hardly occurred between normal discharge and discharge failure, resulting in poor detection accuracy. Further, the detector includes the heating element for adding heat to ink. This complicates and upsizes the printing apparatus, raising the apparatus cost.
In the arrangement disclosed in Japanese Patent Laid-Open No. 2008-000914, the detector is arranged below the heater, so a change between normal discharge and discharge failure is easily detected. However, the temperature drop phenomenon occurs upon contact of a very tiny ink droplet generated in normal discharge, so a large difference is hardly generated between normal discharge and discharge failure. Since the point at which the temperature drop rate changes in normal discharge appears at the timing of a temperature drop, it is difficult to accurately detect the point. As a result, the detection accuracy degrades.